Hwk4A - A reference book on solar energy shows that the...

PHYS 153 Homework 4A Problem 1 A 10 cm diameter, 20 cm long cylinder contains 2 .0 × 10 22 atoms of argon at a temperature of 50 ◦ C. (a) What is the number density of the gas? (b) What is the root-mean-square speed? (c) What is ( v x ) rms , the rms value of the x-component of velocity? (d) Determine the pressure in the cylinder using the ideal-gas law. Problem 2 A 100 cm 2 box contains helium at a pressure of 2 . 0 atm and a temperature of 100 ◦ C. It is placed in thermal contact with a 200 cm 2 box containing argon at a pressure of 4 . 0 atm and a temperature of 400 ◦ C. (a) What is the initial thermal energy of each gas? (b) What is the ﬁnal thermal energy of each gas? (c) What is the ﬁnal temperature? Problem 3 A 10 m × 14 m house is built on a 12 cm thick concrete slab. What is the heat-loss rate through the slab if the ground temperature is 5 ◦ C while the interior of the house is 22 ◦ C? Problem 4 You would like to put a solar hot water system on your roof, but you’re not sure it’s feasible.

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Unformatted text preview: A reference book on solar energy shows that the ground-level solar intensity in your city is 800 W / m 2 for at least 5 hours a day throughout most of the year. Assuming that a completely black collector plate loses energy only by radiation, and that the air temperature is 20 ◦ C, what is the equilibrium temperature of a collector plate directly facing the sun? Note that while a plate has two sides, only the side facing the sun will radiate because the opposite side will be well insulated. Problem 5 A cubical box 20 cm on a side is constructed from 1 . 2 cm thick concrete panels. A 100 W lightbulb is sealed inside the box. What is the air temperature inside the box when the light is on if the surrounding air temperature is 20 ◦ C? 1 - 1...
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